Measuring Atlas Radiation Backgrounds in the Muon System at Startup: A U.S. ATLAS Upgrade R&D Project

Transcription

1 Slide 1 Measuring Atlas Radiation Backgrounds in the Muon System at Startup: A U.S. ATLAS Upgrade R&D Project, Leif Shaver, Michael Starr, Matt Adams ( , undergraduate) THIS WORK IS AN ATLAS UPGRADE R&D PROJECT, FUNDED THROUGH U.S. ATLAS. PEOPLE: Currently, M. Shupe. Later, A. Savine.. We are about to recruit a postdoc who would work part-time time on this project.

2 Slide 2 LHC Upgrade Issues in the Muon System Inner bore of Forward Toroid is a critical thin spot in the current design. May need redesign to reduce background rates after LHC Upgrade. Muon region safety factors are 2-5! 2 Beam pipe is a large background source. May need to be changed to beryllium. 1

3 Slide 3 Aims/Scope of This Project Measure neutron, photon, and charged particle fluxes and spectra in pulsed mode for sensitivity at low luminosity. Compare measured fluxes to Fluka, GCalor, Geant4, etc., then retune simulations. Reduce muon safety factors, for realistic R&D. Monitor sets are at the following C-End C locations: (1) In CSC region, at small r in Small Wheel (2) In TGC1, at small r in Big Wheel (3) In TGC2, at slightly larger r (4) On UX15 endwall,, just outside TAS shield (5) On UX15 sidewall, opposite USA15 All backgrounds are mixed particle types, and broad spectrum.

4 Slide 4 Side Wall to USA15 Monitor Set Locations End Wall 1 CSC TGC2 TGC1

5 Slide 5 Monitor Set, Installed in TGC2 Wheel, July, Six scintillation detectors and one boron-lined proportional tube 3 2 4

6 Slide 6 Monitor Types Scintillators: crystals, plastic wafers, or liquid cells: 1 x 1, coupled to PMT s. Some are doped with boron or lithium for thermal neutron detection. Gas detectors (sealed): proportional tubes with doped gases or linings.

7 Slide 7 Thermal Neutron Detectors (1) Boron lined proportional tube: n + 10 B 7 Li + α Li or α ionize heavily. Pulse-height discrimination minimizes γ and MIP backgrounds. Or, Proportional tube with BF 3 gas: not as radiation resistant as (1), but cleaner signal separation. (2) Boron doped plastic scintillator, on PMT: Same reaction. Run beside undoped counter of same construction. Find n flux by subtraction. (3) ZnS(Ag) plastic scint with 6 Li: Old favorite. Efficiencies are well defined, and rates are easy to extract online.

8 Slide 8 Photon Spectroscopy Atlas test beam background fluxes were measured using a BGO crystal outside iron shielding, and were reported in 2000 by Chris Fabjan, Edda Gschwendtner,, and Helmut Vincke.. They demonstrated that mixed neutron and photon fluxes could be analyzed by convolving ving simulated spectra with the scintillation detector response. Our scintillator choices: (1) LSO Crystal: St. Gobain PreLude 420 (LuYSiO:Ce) crystal: high density (like BGO), thermal stability (unlike BGO). (2) NaI(Tl) Crystal: Will damage sooner, but well understood. Some spectral features can be picked out and reported online. But B full understanding of spectra requires offline analysis by simulation and convolution as with earlier BGO work.

9 Slide 9 Fast Neutron Detectors Fast neutrons in hydrogenic materials scatter elastically, producing slow recoil protons. Threshold ~ 1 MeV. (1) Liquid Scintillator Cell, NE213: PMT pulse-shape discrimination (PSD), is used to separate recoil proton pulses (large slow component) from photon and MIP pulses. PSD requires fast waveform recorders, and is becoming more common practice in the nuclear physics community. (2) NaI(Tl): PSD can be applied to these standard scintillators as well, but the discrimination threshold is higher above 10 MeV. (3) ZnS(Ag) plastic scintillator (undoped): Sensitive to recoil protons. As with photon spectra, this requires detailed offline analysis.

10 Slide 10 Detector Calibration at Arizona All detectors calibrated with Co60 and Cs137 gamma sources. First monitor set also tested with PuBe and Cf neutron sources at Nuclear Engineering. Spectra taken with cable lengths up to 100 m, the maximum needed for installation in ATLAS. LSO Spectrum

11 Slide 11 ATLAS Big Wheel at C End: Radiation monitor sets, TGC1 and TGC2, are near beam in horizontal sectors, between TGC chambers, near the beam on the side nearest USA15.

12 Slide 12 Small Wheel monitors installed on surface Bldg. 190 Same positioning as in TGC1 USA15 side nearest beam.

13 Slide 13 ATLAS DAQ: Local and Remote, Analysis and Monitoring Cavern USA15 Monitor Set 1 e.g. NaI, ZnS, LSO, 10 B prop tube, ion chamber, etc. MUX DMX 2 outpt MCA DAQ PC Set 2 (8) 64 input 5ns,12bit,32Ms Set 3 (8) Set N (8) 64 Channel Discriminate & Scale atlasgw Gain and shaping for pulse height analysis are computer controllable.

14 Slide 14 Fluxes, and Sensor Counting Rates Fluxes in KHz/cm 2 at luminosity n,therm n,fast 34 : γ<10mev γ>10mev h>10mev CSC Region TGC1 Region TAS region EG: 10 B lined proportional tube with A = 70 cm 2, ε =.001, operating at a luminosity of 10 33, counting thermal neutrons, with pulse height discrimination against other backgrounds: CSC: 284 Hz TGC1 : 22.4 Hz Endwall: : Hz Looks reasonable. We are applying this analysis to all sensors.

15 Slide 15 Operating Modes (1) Instantaneous Rates Doped detector raw rates above a threshold. Can be converted to instantaneous flux and sent to Control Room. (2) Fast Turn-Around Around Rates Spectrum features that can be fit above a background, and used to extract instantaneous flux. Can be sent to Control Room, less frequently than (1). (2) Offline Analysis Full spectra are sent to Arizona, and elsewhere, for offline analysis using simulation and convolution to separate mixed backgrounds. These would be used, in turn, to reweight the simulations and reduce the safety factors, making the upgrade simulations ions more precise.. This is, in effect, a test beam run done in situ. (MPX detectors also have this capability.)

16 Slide 16 Status The AZ RadMon DAQ system is cycling through all scintillation detectors taking spectra with various gains and running times. UX15 is one of the least- radioactive places on Earth at the moment, so these are exceptionally dull. We ll see if there is any identifiable activity coming from the special concrete behind the wall-mounted detectors. The proportional tubes will be set up soon.

17 Slide 17 Internet Access Mode? The DAQ computer is connected to the P1 internet, and at present we are accessing it in expert mode to allow for remote software development and commissioning. This status will be revoked as LHC operation nears. At that point we will need a robotic interface (GUI or script) to atlasgw.cern.ch that allows for specification of all run conditions, and controls the outflow of data to the C.R. and elsewhere. It would be preferable to continue to have remote access to the DAQ computer. Is it possible to put it only on the public internet in P1, and then have a robotic process running on lxplus to feed data to the C.R. through a much simplified atlasgw interface?